I would suggest that you go through the tutorials, even though you might not have an interest in making those particular things. It will teach you the basics that you need.
If you just read certain things specific to what you want to make, I think you will confuse yourself more than it will help you. Because those will require that you at least know the basics.
1. Learn the basic way C2 execute a program.
2. Learn what objects are and how to use them.
3. Learn how to pick objects and variables
4. Learn how to use Loops
5. Learn functions
6. Learn how to play sounds.
7. Make you piano